1. Field of the Invention
The present invention relates to a method for recycling a cerium oxide abrasive, and more particularly, to a method for effectively recycling a cerium oxide abrasive used to polish a glass material, such as a glass substrate or a photomask, for reuse of the abrasive.
2. Description of the Related Art
A polishing process is performed to planarize various semiconductor substrates including a glass substrates or a photomask, or the surface of a thin film formed on the semiconductor substrates. Generally, an abrasive is used in the polishing process to improve the polishing efficiency. A variety kinds of abrasives are available, and among them, a cerium oxide abrasive is widely used.
Cerium oxide (CeO2) is a high-function ceramic material used in various applications such as catalysts, fluorescent materials, cosmetics, and the like. A cerium oxide abrasive containing cerium oxide as a main component is used to polish many kinds of glass materials. In particular, recently the cerium oxide abrasive is widely used in electric and electronic appliances such as a glass substrate for an LCD (Liquid Crystal Display), a glass for a recording medium including a hard disc, and the like, and an application range of the cerium oxide abrasive is increasingly expanding.
The cerium oxide abrasive improves the polishing efficiency through a mechanical reaction in a polishing process of a glass material. That is, the polishing efficiency in the polishing process is improved using friction between the cerium oxide abrasive and a polishing pad, and the glass material. Also, the polishing efficiency may be improved through a chemical reaction. That is, a glass or a photomask contains silicon oxide (SiO2) as a main raw material, and silicon oxide exists in the form of Si—OH on the surface of particles in an aqueous solution by a reaction of silicon atoms with OH groups. In this instance, the cerium oxide abrasive chemically reacts with, in particular, bonds with the OH groups in the Si—OH, and then the silicon atoms are detached from the glass or the photomask.
Generally, the cerium oxide abrasive is placed in a slurry tank as a slurry containing cerium oxide, water, and a dispersant, and when a polishing process is performed, the cerium oxide abrasive is fed to a polishing machine. However, the cerium oxide abrasive is high-priced, and is used with a considerable amount in one polishing process. This is the reason why the cerium oxide abrasive is reused throughout several polishing processes. In other words, the cerium oxide abrasive in the type of a slurry is provided from the slurry tank to the polishing machine for use in a polishing process, and then is re-provided to the slurry tank for reuse.
However, the repetitive use of the cerium oxide abrasive in the polishing process results in reduced polishing efficiency of the cerium oxide abrasive. FIGS. 1 and 2 illustrate, respectively, an Si—OH layer 200 formed on and fine powder 300 attached to the surface of a cerium oxide particle 100 after a repetitive use of a cerium oxide abrasive in a polishing process according to a conventional art.
That is, as described above, the cerium oxide abrasive acts to detach the Si—OH structure from silicon oxide, and accordingly, when the cerium oxide abrasive is repeatedly used, the Si—OH layer 200 may be formed on the surface of the cerium oxide particle 100, as shown in FIG. 1. Moreover, the fine powder 300 occurring during a polishing process may be attached to the surface of the cerium oxide particle 100, as shown in FIG. 2. Here, the fine powder 300 may be fine powder of a glass material (SiO2) or cerium oxide (CeO2).
When the Si—OH layer 200 is formed on or the fine powder 300 is attached to the cerium oxide particle 100 as descried above, the cerium oxide abrasive does not have polishing effects any longer. This is because the Si—OH layer 200 or the fine powder 300 reduces the exposed area of the cerium oxide particle 100, thereby hindering mechanical and chemical reactions of the cerium oxide particle 100 during a polishing process. In order to solve the problem, the used cerium oxide abrasive should be replaced. However, as described above, a cerium oxide abrasive is high-priced, and consequently, it causes an increase in a manufacturing cost of a product using a glass material.